The present invention relates to a hemodialysis assist device which may be used in conjunction with a conventional flowing dialyzate fluid hemodialysis device.
The conventional method of treating a person suffering from kidney disease or kidney failure is by use of an artificial kidney machine. Blood is withdrawn from one blood vessel, usually an artery, and subsequently returned into another blood vessel, usually a vein, after passage through a dialyzer which includes a number of separate flow passages for blood and dialysis fluid on opposite sides of a dialysis membrane. However, there is an inadequate number of available artificial kidney machines and trained personnel to operate them. Use of such machines usually requires immobilization of the patient for up to thirty hours per week in the hospital with an average of six to eight hours for each treatment. High level retention of phosphate continuously builds up in the serum of the patient (hyperphosphatemia) because the phosphate ion transfer across the membrane in such hemodialysis treatments is slow. Severe crippling can result from longterm elevations in serum phosphate.
One suggested alternative to a conventional hemodialyzer is set forth in U.S. Pat. No. 3,608,729 (Haselden). There, dialysate fluid is disclosed as being contained in a stationary form on the opposite side of a semi-permeable membrane from the blood. Dialysis fluid-saturated absorbent material is disclosed as being deposited as a compact layer in finely divided form as a filter cake or as a layer of paste away from the flowing blood. The disclosed adsorbent materials include charcoal or an ion-exchange resin. The patent suggests that urease enzyme could be employed to break down urea to form ammonia which is adsorbed by the adsorbent.
The Haselden U.S. Pat. No. 3,608,729 is, as a hemodialysis device for patients in chronic renal failure, deficient in a number of important respects. Firstly, the adsorbent material is deposited as a layer of paste. If it was held in this state, it would tend to block efficient dialysis across the membrane. On the other hand, if the particles loosened, it would tend to settle to the bottom of the apparatus by gravity with insufficient mass transfer contact with the dialyzed components of the blood. Furthermore, the removal of excess body fluids in the blood which accumulate daily could not be performed simultaneously or intermittently with dialysis. That is, application of a vacuum to the dialysis fluid chamber would tend to remove dialysis fluid together with the adsorbents and urease enzyme from the sealed dialysate cavities.
Another attempt at a wearable dialysis apparatus is disclosed in U.S. Pat. No. 3,388,803. This device is contoured to the human body and includes blood inlet and blood outlet conduits formed by semipermeable membranes. On the outside of the tubing is dialysate fluid. Uric acid is the only substance which the patent indicates as being removable from the blood in the dialysate fluid. It is incapable of removing toxic waste metabolites, such as urea, from the blood and suffers from the other deficiencies set forth with respect to U.S. Pat. No. 3,608,729.
In another approach, set forth in a paper by Charles M. Grossman, entitled "Dessicant-Induced Ultrafiltration Across An Artificial Membrane", J. Applied Physiology, 32; No. 2, February 1972, urea is transferred across a membrane into a desiccant compartment. A Sephadex gel is used in the compartment together with urease enzyme and an ion retention resin. The paper indicates that the ammonium ion produced by the urease enzyme is reduced by 90% by using an ion retention resin.
The stated purpose and function of Grossman's Sephadex gel and agar natural gels is to promote water adsorption by means of their desiccant nature. It is well known that Sephadex dextran gel tends to release carbohydrate chain molecules and natural degradation polysaccharide segments, at sizes below average molecular weights of 20-25,000. These molecules can readily diffuse into the patient's blood resulting in pyrogenic action and very harmful immunological responses. Agar gel comprises the collagen protein. Similarly, dangerous pyrogenic and immunological reactions result when collagen fragments and molecules enter into the patient's blood.
Grossman U.S. Pat. No. 3,742,946 relates to the same type of device as the aforementioned article. It mentions that charcoal or zirconium can be used to remove salicylates and barbituates.
None of the above devices using nonflowing dialysate fluid are effective replacements for conventional hemodialysis units. Furthermore, their authors do not suggest the importance of a nonflowing dialysate fluid hemodialysis assist unit for use in conjunction with a conventional hemodialyzer which would reduce treatment time, and treat the problems of elevated serum phosphate and lipid levels in patients. Furthermore, this would reduce cost of treatment by shortening dialysis time thereby increasing the cost-effectiveness of dialysis centers and home dialysis.